Beede, DK

Collier, RJ

Mallonee, PG

Schneider, PL

Wilcox, CJ

English

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198Potassium nutrition ofheat-stressed lactatingdatry cowsD.K. Beede*,  P.G. Mal lonee, P.L.  Schneider,C.J.  Wi lcox and R.J.  Col l ierDairy Science Department, University of Florida,Gainesville, FL 32611, U. S.A.*To whom correspondence should be addressedTwo experiments were performed to assess dietarysupplementation to enhance potassium status and productionresponses of heat-stressed lactating dairy cows. Elevatedtemperatures reduced feed consumption and milk yield. Feedintake and milk yield were higher when 1,08o/o K compared with0,66% K was included in the diet, but not at the 1,64% K level.When supplemental potassium was provided by KHCO, (ratherthan KCI), feed consumption and milk yield declined by 11%.Twee eksperimente is uitgevoer om die invloed vandieetaanvull ing op die verhoging van kalium status enproduksie-reaksie van lakterende melkkoeie wat aan hittedrukonderwerp is, te bepaal. Verhoogde temperature verlaagvoerverbruik en melkopbrengs. Voerinname n melkopbrengswas ho6r wanneer 1,08/o K ingesluit is in die rantsoen, teenoor0,66% K, maar nie op die 1,M1" vlak nie. Wanneerkaliumaanvull ing voorsien is deur KHCO3 (eerder as KCI), hetvoerverbruik en melkopbrengs gedaal met 11%.Keywords: Potassium, macrominerals, heat stress, lactationIntrodustionFlorida lies in a subtropical region (24"32' to 3L'Nlatitude). Environmental heat stress significantly affectsdairy cattle performance annually over a 5 month period.When Black Globe Temperature (BGT), an integratedmeasure of dry bulb air temperature, wind velocity andsolar radiation, rises above 29"C, feed intake and produc-tion are reduced. Many responses to heat stress, such asincreased respiration and sweating rates, are survivalstrategies aimed at maintaining normal body temperature.These typically compromise maximum production andoptimum efficiency (Collier, Beede, Thatcher, Israel &Wilcox, 1982).S.-Afr. Tydskr. Veek. 1983, 13(3)In 1978, 401 Florida dairies averaged 491 cows each,with about 60 dairies having over 1,000 cows (Wilcox,Van Horn, Harris, Head, Marshall, Thatcher, Webb &Wing, 1978). Complete mixed diets are common (60-70%concentrates and 30-40% roughage). Many feeds, par-ticularly cereal concentrates and by-product feeds, maybe low in potassium (less than 0,8% on a dry basis).We hypothesized that heat-stressed lactating cows mayhave higher dietary potassium requirements because of:(a) lactational stress associated with high production andhigh milk potassium content (0,15-0,17%), (b) heat stressowing to increased body potassium loss through sweatingand decreased daily potassium intake and (c) diets oftencontain considerable low potassium feeds. Two experi-ments were performed to assess dietary supplementationto enhance potassium status and production responses ofheat-stressed lactating cows.ExperimentalExperiment IObjectives were to assess production and physiologicalresponses of cows to varying dietary potassium (0,66;1,08; 1,64%; dry basis) when in a no shade (NS) or shade(S) management system.MethodsTen Holstein (mid-lactation) and eight Jersey (early-lactation) cows were blocked by breed and assigned to NSopen lot or S structure with an adjoining open lot(Roman-Ponce, H., Thatcher, W.W., Buffington, D.E.,Wilcox, c., 1977), in a split-plot (NS or S as main plots)with a 3 X 3 Latin Square (period and dietary potassiumlevel) as sub plots. All cows received different dietarypotassium treatments in each 30-day period. Basal dietwas 52% ground corn, 9,5% corn gluten meal, 1,0% urea,34% cottonseed hulls, minerals and vitamins. Potassiumchloride replaced small amounts of corn to achieve ap-propriate potassium treatments. Other nutrients wereformulated to meet 1978 NRC recommendations. Adlibitum feed intake of individual cows was measuredbetween 0800 -1700 and 1700- 0800h daily for the last 2wks of each period. Milk yield was measured twice dailyat (0700 and 1630h) and BGT was monitored hourly from1100-1800h. On day 29 of period 2 sweat secretions werecollected to measure relative skin potassium loss during2 h intervals at 0900, 1300 and 2000h.Results and DiscussionAverage BGTwas 44,1 vs 33,5°C for NS and S. Respirationrate (RR) (132 vs 88/min) and rectal temperature (RT)(41,2 vs 39,9°e) were greater in NS. Dietary potassiumtreatment did not not effect RT or RR. Total daily feedintake was greater in S than NS (21,3 vs 18,7 kg). Daytimefeed intake was depressed 56% in NS (4,0 vs 9,2 kg). NScows consumed increasing amounts of feed as potassiumlevels increased, suggesting higher potassium enhanceddry matter intake (3,7; 4,0 and 4,7 kg at 0,66; 1,08 and1,64% potassium). At night feed intake was 19,5% greaterin NS than S (14,7 vs 12,3 kg) suggesting an attempt tocompensate for reduced daytime intake.Morning milk yield was 23% greater in S (9,6 vs 7,8 kg).Evening yield was 27% higher in S (8,1 vs 6,4 kg).Curvilinear effect of dietary potassium on milk yield wasobserved for morning and evening milkings. Total dailymilk yield was 20% lower in NS (14,2 vs 17,7 kg).Curvilinear effect of potassium on total daily milk yieldwas noted with 0,66; 1,08 and 1,64% potassium of 15,2,16,6, 16,1 kg/d. Milk yield improved as potassium levelincreased from 0,66 to 1,08%. However, increasing thelevel to 1,64% provided no additional benefit. Consideredwithin environment, response to added potassium from0,66 to 1,08% was greater in NS (12% increase) than S(6% increase). This suggested additional beneficial re-sponse to dietary potassium in heat-stressed cows.Figure 1 illustrates the effects of environment on relativeskin potassium secretion rate. The rate was greater in NSthan S in every sampling interval. During peak heat load(1300-1500 h), potassium secretion rate was about 5-foldgreater in NS.Results suggested lactating cows could be in a ratherprecarious negative potassium balance during heat stress.This coupled with major loss of potassium in milk,certainly presents a different osmotic and electrolyteregulation dilemma for cows experiencing heat stress thanfor normothermic cows.50NS••• 40...0(""Z 30Q•....."" 20u...'"100Figure 1 Effect of no shade (NS) or shade (S) environment on relativesecretion rate of potassium from the skin (mg/m2/h).Experiment /IObjectives were to evaluate effects of heat stress,total dietary potassium, dietary potassium bicarbonate(KHC03) and sodium bicarbonate (NaHC03) on pro-duction responses. It was postulated that mineral buffersmight increase efficiency of fermentation by increasingruminal pH. Also, KHC03 might serve as a source ofbicarbonate and supplemental potassium.MethodsExperimental design was a split-plot in which environmentwas NS or S. Within each environment was a 2 X 2 X 2factorial arrangement of eight dietary treatments. Dietarytreatments were 0 and 0.85% NaHC03, 0 and 1.0%KHC03, and 1.08 and 1.63% total dietary potassium.Basal diet was 25% cottonseed hulls, 58% ground corn,10% corn gluten meal, urea, vitamins and minerals.Twenty four Holstein cows in early to mid lactation wereassigned randomly to each environment and dietary200treatment. Cows remained in each environment through-out but received a different dietarv treatment in each ofthree 35 d periods.Results and DiscussionAverage daily BGT (0900- 1600 h) was 29,1oC for S and41,0oC in NS. Rectal temperatures at 1300h averaged39,2"C in S.and 40,8"C in NS. Respiration rates for cowsin S averaged 85 vs 130imin in NS. Respiration rates evenin S indicated hyperthermia, but were lower than in NS.Table 1 shows production responses to dietary treatmentand environment. Environment affected feed intake andmilk yield. Feed intake and yield of cows in S increased by8,6o/o and 4,7"/", with inclusion of NaHCOr. Similar butnot significant trends were observed in NS.Added KHCO3 had a negative effect on feed intakeand milk yield in NS. Lower intake of treatments con-taining KHCO3 might be due to low palatability. In fourtreatments KHCO, contributed about half of the totalpotassium to each (KCl provided the rest). This mayexplain the lower intake in NS at I,63o/" than at 1,08%total dietary potassium. There was a significant inter-action of KHCO, and total dietary potassium on feedintake. Despite lower feed intake with 1,63o/" total dietarypotassium compared to 1,08%, milk yield was higher withhigher total dietary potassium.Table 1 Dietary t reatment and environmentaleffects on production responses, Experiment 2Feed intake (kg/d)" Milk Yield (kg/d)"'bDietary Y" of.Treatment Ration DM Shade No shade Shade No shadeS.-Afr. Tydskr. Veek. 1983, 13(3)In Experiment 2, similar increases were noted in milkyield of NS cows with higher dietary potassium (1,08 toI,63"/"). However, when supplemental potassium wasprovided by KHCO, (rather than KCI), feed consumptionand milk yield declined L7%.ReferencesCOLLIER, R.J., BEEDE, D.K., THATCHER, W.W.,ISRAEL,L.A. & WILCOX, CJ., 1982" Influences of environment and itsmodification on dairy animal health and production. ,I. Dairy Sci.65,2213.ROMAN-PONCE, H., THATCHER, W.W., BUFFINGTON,D.E., WILCOX, C.J. & HEAD, H.H., 1977. Physiological ndproduction responses of dairy cattle to a shade structure in asubtropical environment. J. Dairy Sci. 60,424.WILCOX, C.J., VAN HORN, H.H., HARRIS, B., HEAD,H.H., MARSHALL, S., THATCHER, W.W., WEBB, D.W.& WING J.M. 1978. Large Herd Dairy Management. UniversityPresses of Florida, Gainesville, xiii.NaHCO,KHCO3Total K19,8) 1  5 *2 l , l20,220,720,620,617,815,9*0,000,950,001,001,08r,6316,5 19,0 16,917 ,2 19,9* t7,2L9,3 18,019,6 16,0*Environmental Effects77 ,4 r9,2 16,816,3* 19,7 r7,3*16,8** 19,4 r7,0**I Least squares means.o Feed intake as covariate.' (P < 0,05) significant for dietary treatments only between ap-propriate pairs of means.** (P < 0,01) significant for environmental effects.ConclusionsAs demonstrated by the NS and S model, elevated tem-peratures reduced feed consumption and milk yield,;uggesting altered potassium metabolism and nutritionJue to heat stress. This is probably due to lower feedLntake (and, thus, potassium intake) and greater loss ofoody potassium through sweating in NS compared to Slows. In Experiment 1., increasing potassium from 0,66 tot,08%, increased feed intake and milk yield in NS cows.Flowever, increasing total dietary potassium from 1,08 to1,,64o/" resulted in decreased yield and feed consumption.

Potassium nutrition of heat-stressed lactating dairy cows

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Potassium nutrition of heat-stressed lactating dairy cows

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